1. Field of the Invention
The present invention relates to an ignition timing control device for controlling ignition timing by allowing spark discharge of an ignition plug in an internal combustion engine.
2. Description of Related Art
An ignition timing control device for an internal combustion engine operates to set the ignition timing by allowing spark discharge of an ignition plug at a suitable timing point matched with the operation of an engine. For example, in an acceleration state of an engine in which the rotation of the engine is increased, the control device operates to advance the ignition timing.
However, if the operational state of an engine is shifted from a low rotational state to a rapid acceleration state, the ignition timing tends to more advanced when compared with the ignition timing actually required for the interior of a combustion chamber. This is because of a variation in the air-fuel ratio caused by a rapid change in the throttle valve opening, a variation in the rate of actual rotation of the engine, and the like. Knocking, acceleration shock, and the like may be caused by the above-mentioned conditions.
To solve such problems, Japanese Patent Laid-open No. Hei 1-232169 discloses a method wherein if a variation in opening of a throttle valve of an internal combustion engine is equal to or more than a specific value, it is determined that the operation is a rapid acceleration operation. The ignition timing is therefore retarded, to thereby moderate shock caused by a change in output of the engine upon rapid acceleration.
The above-described prior art method, however, has a problem. Namely, even when the operational state of the engine is shifted from a low rotational state to a rapid acceleration state, if the shifting of the operational state of the engine is performed from an operation in which the throttle valve is gradually opened to an operation in which the throttle valve is rapidly opened, the rotation of the engine increases easily in accordance with an instruction of rapid acceleration. In this case, it is not necessary to retard the ignition timing, and if the ignition timing is retarded in the same manner as when the operational state of the engine is shifted from a state in which the opening of the throttle valve is kept constant to a rapid acceleration state in which the opening of the throttle valve is made to open rapidly, the operational state of the engine is degraded.